<!--在一个标签内的css属性中,添加clear left(right,both,none)表示该标签左侧不能存在悬浮标签 -->
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
<style type="text/css">
         * {
             margin:0;padding:0;
         }
        .container{
            border:1px solid red;width:300px;
        }
        #box1{
            background-color:green;float:left;width:100px;height:100px;
        }
        #box2{
            background-color:deeppink; float:right;width:100px;height:100px;
        }
         #box3{
             background-color:pink;height:40px;
             clear: left;
         }
</style>
</head>
<body>

        <div class="container">
                <div id="box1">box1 向左浮动</div>
                <div id="box2">box2 向右浮动</div>
        </div>
        <div id="box3">box3</div>
</body>
</body>
</html>